This invention relates to a water repellent for application to glass (hereinafter called a glass-grade water repellent) and to water-repellent glass. More particularly, this invention relates to a glass-grade water repellent that exhibits an excellent water repellence and that is particularly well suited for the production of glass whose surface improves the flow of water drops that have come to rest on the glass surface. This invention also relates to water-repellent glass whose surface has been treated with said water repellent.
Glass-grade water repellents are already known in the form of treatment agents based on alkyl-substituted trichlorosilane (e.g., methyltrichlorosilane, ethyltrichlorosilane, or octyltrichlorosilane), perfluoroalkyl-substituted trichlorosilane, or hexamethyldisilazane (refer to Japanese Patent Application Laid Open [Kokai or Unexamined] Numbers Sho 58-142958 [142,958/1983], Sho 58-172246 [172,246/1983], and Hei 2-247914 [247,914/1990]). The trichlorosilane-based water repellents are very reactive with the hydroxyl groups on the surface of glass and therefore offer the advantage of good treatment efficiencies. However, they suffer from the disadvantages of poor storage stability and poor processability because they are quite susceptible to conversion to low-reactivity silanol or unreactive siloxane through their reaction with atmospheric moisture during storage and during handling in open systems. In addition to these disadvantages, the hydrochloric acid produced during treatment of the glass surface is corrosive to metals, which precludes application to glass that will adjoin metal, for example, automotive glass panes. Glasses whose surface has been treated with a trichlorosilane-based water repellent invariably exhibit a contact angle versus water of at least 105xc2x0 and thus an excellent water repellence. However, water drops residing on such surfaces do not readily flow or drain off. In particular, when a spray of water drops attaches to such a surface, a large number of water drops may attach in a particular area and fail to flow off, causing obstruction of the field of vision for a lengthy period of time. The hexamethyldisilazane-based water repellents are encumbered by the high volatility of hexamethyldisilazane itself. When this type of water repellent is spread out on the glass surface, the hexamethyldisilazane volatilizes before it can react with the surface hydroxyl groups, which prevents a thorough development of the agent""s activity. In addition, glass treated with hexamethyldisilazane-based water repellents also suffers from the same problem of field-of-vision obstruction because water drops attaching on such surfaces are again resistant to flow.
In specific terms, then, the present invention takes as an object the introduction of a glass-grade water repellent that is highly processable and is able to yield glass free of vision obstructions because water drops residing on the glass surface readily flow or run off. An additional object of the present invention is the introduction of water-repellent glass whose surface has been treated with the subject water repellent.
The present invention relates to a water repellent for application to glass, comprising disilazane with the general formula 
in which n and nxe2x80x2 are the same or different integers having values from 2 to 20. The invention also relates to water-repellent glass whose surface has been treated with the subject water repellent.
The glass-grade water repellent according to the present invention characteristically comprises disilazane with the general formula given above. The subscripts n and nxe2x80x2 in this formula, which may be the same or may differ, are integers from 2 to 20 and preferably from 4 to 15. The groups xe2x80x94CnH(2n+1) and xe2x80x94Cnxe2x80x2H(2nxe2x80x2+1) are exemplified by ethyl, propyl, butyl, pentyl, hexyl, octyl, decyl, dodecyl, and octadecyl. This group may have either a straight-chain or branched-chain structure, but straight-chain structures are preferred. This disilazane is exemplified by compounds with the following formulas. 
This disilazane can be synthesized, for example, by bubbling ammonia (equivalency=3xc3x97 on a molar basis) through the chlorosilane prepared by the platinum-catalyzed addition reaction between dimethylchlorosilane and the straight-chain alpha-olefin CnH2n and/or Cnxe2x80x2H2nxe2x80x2 (n and nxe2x80x2 are integers from 2 to 20). The ammonium chloride by-product is then removed followed by distillation or elimination of unreacted starting materials.
While the glass-grade water repellent according to the present invention comprises the above-described disilazane, it may contain components added on an optional basis for the purpose of improving its durability and wipe-off characteristics. These optional components are exemplified by powders, such as those of silica, calcium carbonate, magnesium oxide, and so forth, and by low-boiling organic solvents, such as toluene, xylene, and so forth. In the case of organic solvent addition, the resulting disilazane concentration is preferably at least 1 percent by weight and particularly preferably from 5 to 50 of the total composition.
Techniques for treating glass surfaces with the glass-grade water repellent according to the present invention are exemplified by the following: application of the water repellent from paper or cloth impregnated with the water repellent; use of a sprayer to spray a mist of the water repellent according to the present invention; and immersion of the glass in water repellent according to the present invention. The surface of the glass that will receive this treatment is preferably preliminary cleaned with organic solvent or detergent. After the water repellent according to the present invention has been coated on the glass surface by one of these techniques, the treatment is completed by wiping off the excess agent with a dry paper, cloth, etc., and/or by heating.
The glass-grade water repellent according to the present invention as described above is relatively stable to atmospheric moisture and therefore exhibits an excellent processability and storage stability. In addition, since ammonia is the by-product evolved during treatment of the glass surface, the water repellent according to the present invention will not corrode metals and can therefore be applied to glass adjacent to metal, for example, automotive glass panes.
The characteristic feature of water-repellent glass according to the present invention is that its surface has been treated with the above-described water repellent. Suitable glass substrates are, for example, glass panes in the transportation sector, such as in vehicles like automobiles and railroad cars, as well as in aircraft and ships; architectural glass panes; automotive side mirrors; glass for lighting fixtures; glass plate; mirrors; glass containers; glass instruments and appliances; lenses for eyewear; and lenses for optical components. Preferred among these are architectural glass panes and glass panes in the transportation sector.
Water-repellent glass according to the present invention exhibits little difference between its advancing and receding contact angles versus water. As a result, water drops attached on its surface flow much more readily than for glass whose surface has been treated with prior-art glass-grade water repellents. Water-repellent glass according to the present invention is therefore highly qualified for application as glass panes where good visibility is a critical issue.